Review Super-Portable Sennheiser MM 400-X Bluetooth headphones With Excellent Audio

The Sennheiser MM 400-X is a pair of Bluetooth headphones that fold up to a truly portable package. At £179.99 these wireless headphones better be good, as there are cheaper sets out there. See our Best Headphones round-up for more great cans.
Sennheiser MM 400-X Bluetooth headphones design

The lightweight 400-X headphones fold up and can be packed into the included soft travel case, along with a cable should the battery run down or you want to connect to a non-Bluetooth device, such as an in-flight entertainment system. The MM 400-X remind me of my once-favoured Sennheiser PX 200-II headphones that I loved for their portability and sound but had to repeatedly replace due to an inherent weakness in the cable by the jack. I must have purchased four sets before my patience wore as thin as the dodgy jack connection, and moved away from Sennheiser to go cable free with the wireless Bluetooth Creative Hitz WP380 headphones.



The padded ear cushions are soft and comfortable, and as they are so light (105g) you’ll soon forget your wearing headphones at all. You can control your music using the headphones themselves. Pairing the Bluetooth headphones to your music source is easy and all activated on the right earpiece, just like the music controls.

There’s an integrated microphone as well so you can enjoy your music and still not miss that important/nuisance phone call. You recharge the headphones with the supplied Micro USB cable. If you’re on a super-long journey between charging opportunities you can swap out the battery for a spare; available separately for £20. The option of carrying a spare battry is another plus point for the 400-X.

Sennheiser also sells a version of these headphones, with the added benefit of noise cancellation: the Sennheiser MM 450-X costs £249.99. These also utilise Sennheiser’s TalkThrough function, which lets you speak to a neighbour or flight attendant without removing the headset. Just press a button and an external invisible microphone lets you hear everything that is going on around you.


Bluetooth is limited by a maximum available bandwidth so it’s not always suitable for delivering high-quality audio. These headphones use the aptX codec that promises “CD-quality” wireless connection, by significantly reducing the bit rate without affecting audio quality or introducing latency issues.

Tested with the wired cable first, the headphones have a sense of bass depth, and a great kick to drums. There is some upper bass lift here to give a warmer, more exciting sound. Yet the bass is not excessively ramped up to give the urban streetphones effect of Beats, for example.

Andrew felt the midrange a little opaque but in line with rest of sound top to bottom, so well balanced. Voices, male and female, are all still very intelligible and articulate. They boast a gentle and nicely smoothed treble, if a little too dulled for some people’s taste. They won’t reveal the air and presence of some recordings so well, so are not the last word in detail.


We found the audio over Bluetooth with aptX a slightly grittier sound, with more top-end presence. Some music was apparent as more ‘shouty’; and three-dimensionality suffers a little too, as wireless sound is more squashed up. Overall the Sennheiser MM 400-X headphones give a well-mannered, measured presentation of music.

Used with their cable they should prove good headphones for taming the excesses of low-grade MP3 and bright digital recordings. Best of all they have a good, natural ‘musical’ quality that could let you listen for hours without fatigue. Used wirelessly you may lose that easy-going sound and instead hear a grittier, rougher effect in comparison, but that’s one of the trade-offs for the benefits of wire-free headphones, and these are some of the best we’ve tested.